This invention relates to articles constructed of reinforced concrete, and more particularly to locating steel reinforcement fabric or mesh in relation to forms and the like when manufacturing such products.
In the manufacture of pre-cast concrete floors, walls, concrete pipe, manhole sections, and other products, it is well known to employ a steel reinforcement framework such as a flat mesh, woven wire fabric or cylindrical cage. The reinforcement adds tensile strength and otherwise enhances product life and durability. Typical reinforcing frames are constructed of perpendicular rods, bars or wires welded together at their points of intersection. Longitudinal and transverse rods form a flat mesh, and axial and circumferential rods form a reinforcing cage for concrete pipe. The respective intersecting members typically are uniformly spaced apart to provide generally rectangular windows with typical sizes of 2".times.4", 4".times.8", 2".times.12" and numerous intermediate sizes. The rods, bars or wires themselves have diameters ranging from 0.08 to 0.66 inches.
A critical design feature for such products is the thickness of the concrete cover over the framework. In the case of concrete piping or manhole sections, the coverage is determined by the spacing between the reinforcement cage and the outside form or jacket, and in the other direction between the cage and an inside form or core.
To provide a predetermined spacing, self-mounting wire spacers frequently are attached to the reinforcing framework. The spacers have loops or legs of a predetermined length which project outwardly of the reinforcement fabric and abut the jacket or other form to set the proper spacing. One example of such a spacing element is shown in U.S. Pat. No. 3,471,986 (Swenson). The spacer is constructed of flat, relatively thin spring steel and has opposite hooked ends adapted to snap over parallel, spaced apart wires of a reinforcement cage. U.S. Pat. No. 3,722,164 (Schmidgall) shows a spacer with a wrap-around portion for connection to a reinforcement rod, with an opposed portion for hooking around another one of the reinforcement rods, with a spacer leg projected outwardly of the first rod. A steel spacer having a torsion leg is disclosed in U.S. Pat. No. 4,452,026 (Tolliver).
One method of manufacturing concrete piping, known as the packer-head method, requires particularly strong spacer elements. The packer-head method does not employ an inside form or core, but rather utilizes a rotating packer-head to compact low moisture concrete against the outside form or jacket, with the reinforcement cage spaced with reference to the jacket. As it compacts the concrete, the packer-head imparts a substantial rotational force to the cage, and in fact can rotate the cage. The spacer elements must withstand this rotational force, and avoid bending or becoming dislodged from the cage under such force.
The above spacers, however, are too thin for such heavyduty applications, particularly for larger reinforced pipe and manhole sections which can have diameters as large as 9 feet and utilize packer-heads as large as 78 inches in diameter. The Swenson spacer, due to its flat construction, presents sharp edges to the jacket seam during any rotation of the cages in the jacket when the packer-head method of forming is used, and can become dislodged during compacting. A strengthening of this spacer, for example by increasing its size, would render it difficult to mount without special tools. The Schmidgall spacer likewise would be difficult to mount if increased in size to provide the needed strength. This spacer leg ends in an unfinished edge which can damage the jacket and is subject to bending under the forces induced by the packer-head. The Tolliver spacer needs an intermediate rod, bar or other member for support. The spacer disclosed by Tolliver further must be constructed of a 10 gauge or thinner wire, due to its reliance upon torsional forces, particularly in the torsion leg, for mounting of the spacing element. Such mounting, in the case of heavy gauge spacers, could not be accomplished by hand.
The prior art does include heavy-duty spacing elements. For example, in U.S. Pat. No. 3,440,792 (Schmidgall), a heavy-duty spacer is disclosed for setting the distance between two parallel reinforcement frames, with a spacer loop at one end for determining the distance between one of the frames and a form. U.S. Pat. No. 4,301,638 (Schmidgall) discloses a heavy-duty spacer constructed of 3/16" diameter material, with S-shaped hooks at one end and a bight at the other. Due to the strength of the spacer material, a tool is required for acting upon the bight end to install the spacer. This spacer depends upon a consistent, accurate spacing between the transverse rods of the reinforcement framework, so that different size spacers would have to be maintained in inventory to accommodate the various spacings between reinforcement rods. Also, a deviation in such spacing affects the spacing loops and thus can alter the separation between the frame and jacket.
Therefore it is an object of the present invention to provide a means for accurately, easily and inexpensively positioning steel reinforcing frames with respect to forms to facilitate the manufacture of reinforced concrete articles.
Another object is to provide a spacer element which is heavy-duty in construction but conveniently mounted by hand to a reinforcement mesh or cage.
Another object of the invention is to provide a wire spacing element in which elastic deformation occurs in a plane normal to the extension of spacing loop and therefore has minimal effect on the critical spacing dimension or function of the loop.
Yet another object is to provide a sturdy wire spacing element suitable for installation on a reinforcement mesh or cage, regardless of the spacing between adjacent parallel rods in the framework.